The practice of performing balloon angioplasty as a means of opening blood vessels, which are partially or substantially blocked by plaque, is well known. The biggest problem or risk factor in connection with such percutaneous intervention is downstream embolization of material that collects in and on unstable plaque. Either spontaneously or during a coronary intervention where the plaque is being treated, this material, which consists of blood clot and cholesterol emboli fragments is often being shed downstream. The end result of this appears to be micro-infarction of the territory served by the artery being treated. This, in turn, leads to a heterogeneity of electrical conduction and the creation of a myocardial substrate that makes the patient prone to ventricular arrhythmias, namely ventricular tachycardia or fibrillation. This may explain the small incidence of cardiac death that occurs late after coronary intervention.
As a result of the foregoing, it has been proposed to utilize some form of filter or catcher to collect the particles and debris that tend to break loose. Various approaches have been proposed, such as hanging a basket, a filter or an umbrella on the guidewire, but none seem to work. The reason is that they don""t totally occlude the blood vessel and thus some of the debris gets by. It has been proposed to insert a balloon on a guidewire, which occludes the vessel and then an export catheter is brought down the guidewire, after the intervention and the blood that has collected upstream of the balloon is suctioned out. The problem with this approach is that, while the balloon is inflated, there is no blood flow downstream. The time during which the vessel is occluded is at least about four minutes and this may pose a real risk to the patient. Much longer intervals are likely, if for any reason, the intervention does not go well.
Thus, there is a need for a device and process which can provide a reasonable assurance of catching and removing such debris from blood vessels without significant added risk to the patient.
It occurred to the applicant that what was needed was a double walled balloon having a filter on its downstream end placed downstream of any such intervention. The balloon would conform to the inside dimensions of the artery to block any bypass flow, thereby forcing all of the blood flowing downstream from the intervention through the hollow interior of the double walled balloon to the filter. The debris would be captured on the upstream side of the filter, while permitting an adequate amount of blood to flow downstream through the filter.
Since the double walled balloon must be inflated and deflated, applicant has designed the double walled balloon to be supported on the shaft of a 0.014 nitinol tube. The nitinol tube performs as would a normal solid core guidewire, but the central channel permits inflation and deflation of the balloon with radiographic contrast, and thus facilitates visual positioning under fluoroscopy. When the upstream intervention has been completed the balloon is deflated, thereby trapping the debris inside the two cisterns of the balloon filter. The balloon-filter can then be withdrawn from the artery and the debris examined.
Thus, although the double walled balloon and filter totally occlude the artery except for the filter, there is substantial surface area at the mesh or filter, and one can perform many possible intervention processes upstream, since the filter can catch and trap -any debris resulting from such processes. Additionally, if multiple sequential interventions are performed upstream, the balloon filter may be deflated and reinflated and the debris remains trapped in the cisterns. The deflation cycle facilitates blood flow downstream.